Manipulating micro- and nano-particles with optoelectronic tweezers with large optical spots

The ability to handle and manipulate individual bacteria or human cells can help scientists examine them in detail and understand how they work. Optoelectronic tweezers are capable of this task, but they typically require a very small focused laser spot to function, which necessitates a complex optical setup. Zaman et al. developed an optoelectronic tweezer design that can hold on to and move micron-sized particles without using a very small laser spot.

Most optoelectronic tweezers use a uniform background field and when light, such as a focused laser, hits a photoconductor layer, the disturbance in the uniform electric field would generate forces that are used to manipulate micro- or nano-particles. In effect, a particle gets trapped around the rim of a light spot, and in these designs, the smaller the light spot, the smaller the things you can manipulate.

“In our design, we utilize a non-uniform background electric field that forces a particle along one axis of the optical spot,” said author Mohammad Asif Zaman. “Thus, even if you use a large optical spot, you can hold onto a particle along one axis around the spot. Therefore, you can achieve higher resolution for a given spot size.”

Manipulating micro or nano-sized objects has applications in many scientific fields including biology, medicine, and chemistry. Having a chip or device the size of a quarter that is cheap and easy to manufacture paves the way for rapid advancements in biotechnology. The authors hope the technique can be incorporated into a conventional microscope like those used in bio-research labs for imaging.

Source: “Optoelectronic tweezers with a non-uniform background field,” by Mohammad Asif Zaman, Punnag Padhy, Yao-Te Cheng, Ludwig Galambos, and Lambertus Hesselink, Applied Physics Letters (2020). The article can be accessed at https://doi.org/10.1063/5.0020446 .